How Do Lie Detectors Work?

By November 7, 2013Gadgets

How Do Lie Detectors Work?

We know the scene: it’s the end of the episode and our detective hero is trying to catch the criminal. As a last minute effort, our detective hooks the criminal-in-question up to a Polygraph machine and begins asking a series of questions. We see a close up of a roll of paper charting the readings from the machine’s sensors. “Did you or did you not do it?” asks the detective. “I’m innocent!” insists the criminal. A spike in the reading. “That’s not what it shows here,” smiles the detective. “I will ask one more time: Did you or did you not do it?” The criminal breaks down into confession as the spikes in the machine’s detections go off the charts. Case closed.

Also known as a polygraph test, a lie detector is composed of four to six sensors attached to various points of a person’s body to monitor their pulse, breathing rate, perspiration, and blood pressure. These responses are all involuntary changes that occur when a person undergoes the stress of lying.

An examiner usually starts with irrelevant questions to establish a base to compare against for other answers. These questions usually have known answers and are yes/no or true/false questions such as “Have you ever eaten ice cream?” to establish a normal response reaction. The examiner than moves onto comparison questions which are not related to the potential lie itself, but still make the person in question uncomfortable and feel guilty. The answers to these questions are often already known and may be something like “Have you ever been arrested?” or “Do you own a gun?” Finally, the examiner asks relevant questions and compares the responses to the readings of the comparison questions.

What Does the Lie Detector Actually Detect?

A polygraph doesn’t actually know whether or not you are telling the truth, but it measures basic bodily functions that change drastically when the body is under stress. For most people, telling a lie increases anxiety and stress levels because they do not want to be caught in their lie and they have to focus to make sure their story is sound. A polygraph is basically a fancy stress recorder to detect common symptoms of stress: increased pulse, higher breathing rate, higher blood pressure, and perspiration.

Do Polygraph Tests Actually Work?

This is the most controversial question when it comes to Lie Detector tests. The theory is that most people have enough moral fiber that they cannot escape the stress associated with lying, however there are certainly ways to cheat the system, and there are certainly factors that can contribute to a false reading. Some people can train themselves to control their stress symptoms by altering their breath or manipulating their emotions during test questions (what is your name? what is your favorite color?). Mind tricks are the best way to pass a lie detector test. Some individuals will prick their tongue or put a pin in their shoe so they exhibit the same emotion as each question is asked. Another problem with lie detector test is the fact that some may exhibit stress symptoms simply by being subjected to a polygraph test, so even if they are telling the truth, they become nervous and get suspicious readings on the lie detector test. For this reason, Polygraph tests are excellent tools to use as part of investigation, but they are not often used as the sole way of determining whether or not someone is lying. A polygraph helps you obtain more evidence however, should not be used as the sole factor in finding evidence and the truth.

How Do Lie Detectors Come into Play in Court?

We know lie detectors from pop culture references in movie or TV show courtrooms and investigations, but due to their questionable level of accuracy, polygraph tests aren’t usually a main point of contention in legal cases. It is up to the individual judge of a case to decide whether or not polygraph tests are admissible as evidence. In some cases such as military courts, polygraph tests are actually outright banned. They can be used in police questioning as a basic means of evidence or a strategy to push a confession, but if they are used as evidence in court, both sides usually must approve it and the error rate of the test must be clearly presented. The U.S. legal system has not fully embraced the polygraph test. A polygraph watches you breathe, your heartbeat, and your fingers sweat. Because of this, the court realizes that you cannot solely brand someone a liar for simply having a nervous reaction.

Are Polygraphs Only Used for Criminal Investigations?

When we think “lie detector” we think of intense criminal investigation, but Polygraph tests are also used by a wide variety of businesses for pre-employment screening (though this is often in the government sector), for commercial theft investigations (used by businesses to determine whether or not an employee has stolen money or information or how loyal they are to the company), as part of parole programs (especially for sex offenders) to prevent offenders from committing further crimes, by banks (since bank employees often deal with large amounts of money, it’s important to check in with employee honesty), and even as part of marriage and family counseling (to determine if someone is still cheating, committing an affair, etc.) However, it’s important when conducting lie detector test for any means to make sure that it is done completely legally, with modern and computerized equipment, and with a certified examiner.